I've been lucky over the last few weeks, and sales have really picked up. Of course, I hadn't really started listing things until the last couple of months either.
Now that I'm listing, I realized - my books aren't as in good order as they need to be. I kept okay books - I knew when I had bought stuff, and how much I bought it for. But I realized it was time for a complete overhaul. I also needed to go through and do a complete inventory (again) to make sure I had everything in the right place, and tracked. And to make my life easier when it comes time to filling orders.
So, while I've been following all the excitement over the last few weeks, I've also been busy getting all my receipts in order (or printed or digitized). I've been updating my spreadsheets into nice little monsters, with nice summaries of my current status. I've been tying sales and purchases to specific receipts and invoices (thank you eBay).
What hit me was the amount of sales I was doing, and realizing that this is now a legit business - eBay and Paypal are going to be reporting me, so I better make sure everything is airtight.
Don't wait until it's tax time. Get on your books now, and make sure, if you're really in, you're all in.